On Friday, September 15, Apple will be allowing customers to pre-order not only its new iPhone 8 and iPhone 8 Plus, but also its new Apple Watch Series 3 and the Apple TV 4K set-top box. And on September 22, all of those new devices, which were unveiled at the company’s press event on Tuesday, will be available on store shelves.

But although Apple (AAPL) discusses its features and availability plans for the new devices, the company rarely spends time on stage explaining how the pre-order process might go. And with a new cellular version of the Apple Watch Series 3 now available, the company’s smartwatch will be offered in more places than you might expect.

Get Data Sheet, Fortune’s technology newsletter

Read on for a look at how to pre-order the Apple Watch Series 3. And when you’re done, here’s a guide on pre-ordering the iPhone 8 and iPhone 8 Plus.

When the Clock Starts

Apple’s website doesn’t say exactly when Apple Watch Series 3 pre-orders will begin on September 15, but wireless carriers say they’ll have units available at 3 a.m. ET. So it’s likely Apple will have the same.

Know Your Desired Version

There are lots and lots of Apple Watch Series 3 versions, including those that come with cellular connectivity and those that don’t, as well as different finishes and watchband options. You’ll also need to decide whether you want the 38mm case or the 42mm case.

Time is of the essence with pre-orders, so consider going to the Apple Watch page now to determine exactly what kind of configuration you want. It could mean the difference between getting an Apple Watch Series 3 on launch day or missing out on the initial stock.

Apple Store First

Apple, of course, is offering a pre-order option on its site. Simply go to the Apple Watch page and choose your desired configuration. Apple will walk you through the process, including determining what version of the smartwatch you want and which carrier you’d prefer, if you pick the cellular version. You’ll also be able to make your payment at the end of the process.

Apple Store App Is Useful

Apple’s free Apple Store app is another handy way to make pre-orders. You need only to download the app from Apple’s App store and boot it up when you’re ready to make your order. You’ll go through the process of ordering just like you would online, but if you’re already an Apple Pay user, you can verify a purchase through that mobile-payment service without ever needing a credit card to complete the transaction.

Carriers Have Stock

All four major U.S. carriers—AT&T, Verizon, T-Mobile, and Sprint—will also be carrying Apple Watch Series 3. However, be aware that they’ll only have cellular versions of the device, so if you want a Wi-Fi-only model, they’re not your best bet.

Before you choose a carrier, you should be aware that the Apple Watch Series 3 uses the same number you have attached to your main smartphone line. So, if you’re currently a Verizon customer but think an AT&T Apple Watch Series 3 would be a good idea, you’d need to port your smartphone to that carrier network to get Apple Watch calling support.

It’s a good idea, then, to stick with your existing carrier.